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DYNamics of Architecturally COmplex Polymers

Final Report Summary - DYNACOP (DYNamics of Architecturally COmplex Polymers)

DYNACOP's goal was to obtain a fundamental understanding of the flow behaviour and dynamics of blends of topologically complex macromolecular fluids ( The complex dynamics of these fluids affects the processing and materials properties of myriad nanostructured materials; e.g. instability in extrusion leads to imperfect plastic parts. Prediction of this behaviour based on molecular details has led to academic-industrial collaboration. For example, theory can successfully predict the rheology and molecular features of melts of monodisperse comb-shaped polymers or polydisperse branched polymers. However, significant challenges remain before these new molecular design tools can transform the industrial design process: the tube model must be extended to smaller scales; ring polymers, "branch point hopping" and "constraint release" are poorly understood; and predictive modelling is fragmented into several approaches. Teams comprising synthesis, theory & modelling, and experiments addressed these challenges, while Expert Visiting Fellows (VFs) provided complementary expertise and training.

Thus, the scientific objective was to understand the flow behaviour and dynamics of blends of topologically complex molecules, and their role in processing and properties.The training objective was to train young researchers in the interdisciplinary field of soft matter, to later lead the knowledge transfer to European industry. The socio-economic objective is to provide a strong basis for intelligent engineering of such materials, which is key to the future of numerous European industries. The technical objective is to apply this knowledge, using trained multidisciplinary teams, in polymer-based high-technology industry.

All Early Stage Researchers (ESRs) Experienced Researchers (ERs) were successfully hired at an early stage in the programme, from Asia, Europe, Africa, and North America; the two industrial ERs were hired in the last year of the program. As training the researchers helped coordinate and guide the important activities of Dissemination, Training, Industrial Liaison, and Scientific Planning.

During the project there were numerous courses, including three week-long training courses in Leeds (on generic skills and specific topics such as polymer chemistry, rheology, basic scattering, fundamental and advanced theory of polymer dynamics, etc), laboratory courses in dielectric spectroscopy (San Sebastian) and neutron scattering (Jülich/Garching), a training course at FORTH (Crete), and a two week summer school on entangled and branched polymer science (Capri). The major summer school in Capri in July 2011, organized by the Naples node, comprised seven days devoted to polymer dynamics, followed by an open international workshop co-organized through CECAM, devoted to current topics in entangled polymers. Our Visiting Fellows all came and were integral to both the School and Workshop, and the event was enormously successful. Visiting Fellows played a major role in these two events, and indeed to all events.

Open scientific meetings were held in San Sebastian, FORTH, Capri, and Leeds, with DYNACOP and external scientists. There were two industrial workshops hosted by our partners Dow and BASF, which were in many respects organized by the ESRs and ERs, which gave the Fellows an excellent opportunity to learn about industrial science firsthand, and further develop the skills necessary to be future leaders. The final network-ending conference in December 2012 in Leeds, and was notable in featuring high quality talks from the ESRs, which demonstrated the skills they have received in presentation and communication, as well as the deep command they have of the area of polymer dynamics. The external speakers included a number of very high profile scientists who presented complementary and new areas of science that served as examples of the continued excitement the field still presents.

As of project completion the ESRs/ERs have written and published at least 23 papers, and many more are in preparation, in submission, or will follow after further analysis. The ESRs/ERs were all well-trained in both their specialties, as well as in the wider areas of science associated with the project. During their time they conducted numerous exchange visits with other labs in the project, including those of the Visiting Fellows, in which they experienced the different training and scientific atmospheres available across the network, and made use of specific equipment and expertise.

The scope of scientific accomplishments was great, and spanned the areas of synthetic chemistry and characterisation, experimental design and execution, and theory and simulation. A hallmark of this was the great collaboration among the scientists and institutions.

Synthetic Chemistry -- Anionic chemistry based polymerization capabilities at Durham and Athens have made possible synthesis of a variety of complex architectures and multiblock chemistries; such materials are key for making complex polymer materials with multiple functions and properties. The introduction of novel separation techniques such as TGIC has made possible better separation of these complex polymers. Durham generated hyperblocks (a novel class of branched thermoplastic elastomer) and some symmetric, asymmetric stars with precise long arm short arm ratios, while the Athens group synthesized a variety of architectures ranging from linear to multi- armed stars to exact comb architectures with multiblock/multicomponent control over their chemistry. These partner institutes hence provided pure well-characterized samples of novel polymers to the rheological and other mechanical properties at experimental nodes in the network.

Experimental studies -- The extensional and shear rheology measurement capabilities at FORTH and DTU and the SANS/NSE facilities at FZJ gave a unique combination of experimental expertise to this research network. FORTH studied the rheology of different architectures such as ring polymers, extensional hardening in combs (developing understanding of the effect of arm and backbone molecular weight on amount and onset of strain hardening) and a novel class of dendronized polymers. DTU (Denmark) performed systematic extensional rheology (steady state and relaxation behavior) measurements with their unique filament stretching rheometer (FSR) on monodiperse to polydisperse linear and branched polymers. FZJ (Jülich) determined structural relaxation behavior using SANS and NSE in blends of Cayley trees in a linear matrix and a class of supramolecular polymers to determine their architectural conformations at different conditions, and also explored how intriguing viscosity reduction and reinforcement effects depend on the particle to polymer chain size ratio in polymer nanoparticle composites. Together the polymer physics performed in these groups has led to continued better understanding of steady and non-linear dynamics of different polymer architectures, which is crucial for increasing the processing capabilities of EU (and worldwide) industries, and widening the scope of advanced materials for a multitude of chemical, medical, personal care, and food applications (to name just a few).

Theory and simulation -- The computational and theoretical activity DYNACOP ranbged from atomistic simulations of many individual chains to "tube" models for investigating continuum level fracture-like behavior in monodisperse polymer melts. The atomistic and coarse-grained simulations conducted at UPV (University of the Basque Country) and UT (University of Twente) helped uncover (and understand better) the fundamental mechanisms of stress relaxation and dynamics of different polymer architectures. The atomistic-scale simulation study by UPV helped refine the tube-theory based models for stars and Cayley trees (in collaboration with Leeds), to include a local constraint release mechanism leading to early tube dilation due to “diving modes”, where the branch point can move into the tube segments of one of the branches in addition to the conventional arm retraction motion. An additional model to include entanglement stripping which can reproduce the stress overshoots in elongational flow of polydisperse branched polymers was developed at University of Leeds. Further, the fracture-like behavior of monodisperse linear polymers, which has raised questions regarding the validity of tube theory, was understood using numerical calculations of a standard tube-based constitutive equation.

The work at Dow is directed towards leveraging these fundamental theory based tools for industrial product design by predicting rheology of virtual ensembles that expand the existing product families. Systematic exploration of different architectural and distributional variants of existing products may result in optimal product properties. BASF also

The socio-economic objective, which relies on influencing and interacting with our industrial partners, had substantial progress via the two Industrial Workshops. Moreover, the scientific results have also helped build the intelligent engineering platform foreseen by the project, with examples including advanced characterization techniques (TGIC, neutron scattering methods), unexpected results in the behaviour of ring polymers and entangled melts under step strain, and new understanding about polydisperse melts, which is crucial for real industrial processing. Similar, the technical objective of using multidisciplinary teams to influence engineering design within the EU materials sector is being realized through the collaboration networks of ESRs and ERs, which span synthetic chemistry, characterization and measurement, theory, and computational modelling.

Hence, the project successfully executed its goals of training a new cohort of students for the next generation of academic and industrial science. A key reason behind this was the close interaction that was fostered from the first event in Leeds in which students from all over the world met each other for the first time. A close camaraderie was evident, and this continued throughout the project, and outside the project when “Dynacoppers” would gather at rheology conferences scattered around the globe. Such gatherings will surely happen in future as the team increase their breadth and depth of their contributions to the field.